In the magneto-optic recording process, a vertically magnetizable recording layer is initially sensitized by simultaneously subjecting it to a uniform magnetic field and a temperature which exceeds its Curie temperature (e.g., 400 degrees C.). The magnetic field, being directed perpendicular to the recording layer, serves to uniformly align all of the magnetic domains therewith. Once all the magnetic domains are facing in the same direction, the recording layer is ready to record information. Such recording is effected by subjecting the recording layer to a magnetic field of reverse polarity while scanning the layer with an intensity-modulated laser beam. During the recording process, a laser beam intensity is switched between high and low levels, representing the digital (binary) information being recorded. Only the high level is sufficiently intense to raise the temperature of the irradiated portion of the recording layer to above its Curie temperature; thus, digital information is recorded at the point of incidence of the laser as the more intensely irradiated magnetic domains flip in orientation to align themselves with the magnetic bias field. Playback of the recorded information is commonly achieved by scanning the information tracks with a plane-polarized beam of radiation and monitoring the reflected beam for shifts in the plane of polarization, as produced by the well known Kerr effect. To erase the recorded information, the polarity of the applied external magnetic field is reversed, and the recording layer is scanned with a beam of sufficient intensity to again heat the recording layer to above its Curie temperature. After this erasure step, all of the irradiated magnetic domains will again face in the same direction. Various schemes have been proposed to achieve the magnetic field inversions required in switching between the record and erase modes of the magneto-optic recording process. In the disclosure of U.S. Pat. No. 5,710,747, for example, the field inversion apparatus consists of a permanent magnet induced for movement by a magnetic field produced by electrical coils.
Although the presently known and utilized device is satisfactory, it is not without drawbacks. The coils are positioned directly beneath the recording layer so that heat generated from coils passes upwardly toward the recording layer. Since the digital information is recorded by heat intensity of the laser beam, extraneous heat sources near the recording layer may be undesirable.
Consequently, a need exists in the construction and mode of operating the bias-field device so as to overcome the above-described drawbacks.